Purpose\ud \ud – The purpose of this paper is to assess the prevalence and nature of presentation of unipolar depression in individuals with Prader-Willi syndrome (PWS). \ud \ud \ud \ud \ud Design/methodology/approach\ud \ud – The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (2009) checklist for systematic reviews was followed where possible. \ud \ud \ud \ud \ud Findings\ud \ud – Seven studies were included in the qualitative synthesis from a total of 261 records identified. The quality of the studies was then assessed: scores for each study design ranged from between 3 and 6 of a possible score total of 6. The frequency of depression ranged between studies from 4 to 22 per cent. four studies showed over 50 per cent of patients appeared to suffer from psychotic symptoms. Low mood, anhedonia and irritability were described as features of depression, although no fixed pattern of psychopathology arose from across the studies (excluding psychosis). This review has provided evidence to suggest that depression is a frequent occurrence in the PWS population. One study found that the incidence of depression differed between the genetic subtypes, raising questions regarding the relationship between genotype and behavioural phenotypes. A high proportion of individuals with depression suffered from psychotic symptoms. \ud \ud \ud \ud \ud Research limitations/implications\ud \ud – The small number of heterogeneous studies included in this study precluded meta-analysis of the results. This highlights the need for further original research in this field. \ud \ud \ud \ud \ud Practical implications\ud \ud – An increased awareness of the frequency of depressive symptoms within the PWS population will aid in the timely diagnosis and management of the disorder which will reduce psychiatric morbidity. The noted high proportion of psychotic symptoms associated with depression should raise the index of suspicion with clinicians and aid appropriate management decisions. \ud \ud \ud \ud \ud Originality/value\ud \ud – This review has provided preliminary evidence for the nature of presentation of unipolar depression in PWS. It has highlighted the possibility of an increased propensity towards depression with psychotic symptoms. There is some suggestion of a differing presentation and course of unipolar depression between the common genetic subtypes of PWS which warrants further investigation.